On Wed, Mar 6, 2024 at 6:04 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Mon, Mar 4, 2024 at 10:44 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> >
> > Add three new kfuncs for the bits iterator:
> > - bpf_iter_bits_new
> > Initialize a new bits iterator for a given memory area. Due to the
> > limitation of bpf memalloc, the max number of bits that can be iterated
> > over is limited to (4096 * 8).
> > - bpf_iter_bits_next
> > Get the next bit in a bpf_iter_bits
> > - bpf_iter_bits_destroy
> > Destroy a bpf_iter_bits
> >
> > The bits iterator facilitates the iteration of the bits of a memory area,
> > such as cpumask. It can be used in any context and on any address.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > ---
> > kernel/bpf/helpers.c | 117 +++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 117 insertions(+)
> >
> > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > index a89587859571..a769561b65ae 100644
> > --- a/kernel/bpf/helpers.c
> > +++ b/kernel/bpf/helpers.c
> > @@ -2545,6 +2545,120 @@ __bpf_kfunc void bpf_throw(u64 cookie)
> > WARN(1, "A call to BPF exception callback should never return\n");
> > }
> >
> > +struct bpf_iter_bits {
> > + __u64 __opaque[2];
> > +} __aligned(8);
> > +
> > +struct bpf_iter_bits_kern {
> > + union {
> > + unsigned long *bits;
> > + unsigned long bits_copy;
> > + };
> > + u32 nr_bits;
> > + int bit;
> > +} __aligned(8);
> > +
> > +/**
> > + * bpf_iter_bits_new() - Initialize a new bits iterator for a given memory area
> > + * @it: The new bpf_iter_bits to be created
> > + * @unsafe_ptr__ign: A ponter pointing to a memory area to be iterated over
> > + * @nr_bits: The number of bits to be iterated over. Due to the limitation of
> > + * memalloc, it can't greater than (4096 * 8).
> > + *
> > + * This function initializes a new bpf_iter_bits structure for iterating over
> > + * a memory area which is specified by the @unsafe_ptr__ign and @nr_bits. It
> > + * copy the data of the memory area to the newly created bpf_iter_bits @it for
> > + * subsequent iteration operations.
> > + *
> > + * On success, 0 is returned. On failure, ERR is returned.
> > + */
> > +__bpf_kfunc int
> > +bpf_iter_bits_new(struct bpf_iter_bits *it, const void *unsafe_ptr__ign, u32 nr_bits)
> > +{
> > + struct bpf_iter_bits_kern *kit = (void *)it;
> > + u32 size = BITS_TO_BYTES(nr_bits);
> > + int err;
> > +
> > + BUILD_BUG_ON(sizeof(struct bpf_iter_bits_kern) != sizeof(struct bpf_iter_bits));
> > + BUILD_BUG_ON(__alignof__(struct bpf_iter_bits_kern) !=
> > + __alignof__(struct bpf_iter_bits));
> > +
> > + if (!unsafe_ptr__ign || !nr_bits) {
> > + kit->bits = NULL;
> > + return -EINVAL;
> > + }
> > +
> > + kit->nr_bits = 0;
> > + /* Optimization for u64/u32 mask */
> > + if (nr_bits <= 64) {
> > + err = bpf_probe_read_kernel_common(&kit->bits_copy, size, unsafe_ptr__ign);
>
> it probably would be better to zero-initialize kit->bits_copy?
will do it.
> but also, please check that this works on big-endian right
will check.
>
> > + if (unlikely(err))
> > + return -EFAULT;
> > +
> > + kit->nr_bits = nr_bits;
> > + kit->bit = -1;
> > + return 0;
> > + }
> > +
> > + /* Fallback to memalloc */
> > + kit->bits = bpf_mem_alloc(&bpf_global_ma, size);
> > + if (!kit->bits)
> > + return -ENOMEM;
> > +
> > + err = bpf_probe_read_kernel_common(kit->bits, size, unsafe_ptr__ign);
> > + if (err) {
> > + bpf_mem_free(&bpf_global_ma, kit->bits);
> > + return err;
> > + }
> > +
> > + kit->nr_bits = nr_bits;
> > + kit->bit = -1;
> > + return 0;
> > +}
> > +
> > +/**
> > + * bpf_iter_bits_next() - Get the next bit in a bpf_iter_bits
> > + * @it: The bpf_iter_bits to be checked
> > + *
> > + * This function returns a pointer to a number representing the value of the
> > + * next bit in the bits.
> > + *
> > + * If there are no further bit available, it returns NULL.
> > + */
> > +__bpf_kfunc int *bpf_iter_bits_next(struct bpf_iter_bits *it)
> > +{
> > + struct bpf_iter_bits_kern *kit = (void *)it;
> > + u32 nr_bits = kit->nr_bits;
> > + const unsigned long *bits;
> > + int bit;
> > +
> > + if (nr_bits == 0)
> > + return NULL;
> > +
> > + bits = nr_bits <= 64 ? &kit->bits_copy : kit->bits;
> > + bit = find_next_bit(bits, kit->nr_bits, kit->bit + 1);
> > + if (bit >= kit->nr_bits)
>
> zero out nr_bits so subsequent next() calls keep returning NULL
> (sticky iterator behavior)
Good suggestion. will change it.
--
Regards
Yafang
